There is an existing need for sensors and monitoring schemes for high temperature and harsh environments to address a broad range of applications such as, for example, fossil-based power generation, industrial manufacturing, aerospace/aviation, and the like. Some specific applications for such sensors and spectroscopic techniques include advanced combustion, solid oxide fuel cells, gas turbines, boiler systems, chemical looping, etc. A common need in all cases is the ability to monitor critical process parameters under in-situ conditions which may involve temperatures ranging from, but not limited to, 500-1500° C. (as well as different temperature ranges) depending upon the application of interest. Hydrogen-based energy generation systems such as solid oxide fuel cells are attractive alternatives to conventional thermal based power generation such as through coal combustion, for example, due to their relatively low environmental impact and the potential for higher efficiencies. However, there is a definite lack of sensors that can provide fast in-situ systemic hydrogen utilization feedback at high temperatures such as above 500° C. Although, in general, any temperature can be viable for emissivity monitoring, and is only limited by the availability of detectors and the thermal emission profile of the material in question, which would dictate the choice of the material constituents. Therefore, the proposed method can be ubiquitous across a large span of temperatures.
Optical-based sensing methodologies have emerged as a superior technology for harsh environment sensing due to a number of associated advantages relative to more traditional electrochemical and electrical-based sensing approaches. Such advantages include the lack of electrical wiring or components at the sensing location, mitigated risk of electrical sparking in flammable gas environments, and the ability to perform broad/multiple wavelength and/or distributed interrogation of sensor devices and materials, as material interactions with light provide a much richer parameter space. Although optical-based sensing methodologies have a number of inherent advantages, a key weakness is often the need for an optical light source which can be costly and in some cases can present inherent instabilities over time that must be addressed. While relatively low-cost solutions do exist such as inexpensive halogen sources and photodiodes, it would be advantageous to eliminate the need for a light source to greatly simplify the optical sensor design and to reduce overall costs.
Thermal emission enhancement and thermal spectra tailoring have been observed in a variety of materials some of which are micro/nanostructured, heavily doped semiconductors, rare earth doped, quantum dots embedded, and in tandem with nano-gaps to extract the extraordinary near-field thermal emissions. While these techniques can greatly improve on the overall thermal emission and address desired aspects such as spectral specificity using up-conversion, photonic-bandgaps, and isolated decay channels for application such as in Thermophotovoltaic (TPV) systems, it has not previously been demonstrated that the thermal emission of a material can be significantly altered by changes in the gaseous chemistry of its environment at elevated temperatures. Aside from the basic considerations outlined in the well-known Kirchoff's relationship between emissivity and absorptivity of matter in thermal equilibrium, the current thermodynamic literature does not discuss how the microscopic material constituents are related to variations in thermal emission and how this may be affected by changes in the chemical constituents of complicated environments that exist in many systems such as in energy conversion applications. For example, a Thermophotovoltaic or Thermoelectric system could also see an efficiency enhancement due to placement of the system or some portion of the system in a chemical environment altering the system's chemical, physical, or electrical property, as contemplated for spectroscopic applications.